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How do I label a contour plot in the same colors as the contour lines?

Asked by Heidi Hirsh on 24 Oct 2017
Latest activity Commented on by Yair Altman on 12 Nov 2017
I am hoping to create a contour plot with each line labeled in the same color as that line. I have found instructions for doing this in Python but cannot find the relevant code for matlab.
This is the code I found online (for Python I think): http://python4esac.github.io/plotting/matplotlib.html

  2 Comments

There is a hint that this might perhaps be possible. The contour object, h, has a hidden property LabelTextProperties, that has a ColorData field that is maybe changeable to a color table. The problem with that is that because it is a hidden property, there is no good way to set the property.
The contour object has a java() method that allows you to dig into the java representation. That includes getting the children objects, which are various text and line objects and a couple of other things I have not explored. I have no yet found any way to change the color of the text objects (just of the line objects.)
I all else fails, you could just insert text objects with a white background. This would require a lot of manual labor to properly align and rotate, and would break the moment you decide to resize your plot. So really a last ditch effort.

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1 Answer

Answer by Yair Altman on 25 Oct 2017
Edited by Yair Altman on 25 Oct 2017
 Accepted Answer

There is no need to use Java, just to use the two hidden (undocumented/unsupported) properties TextPrims (the text label handles) and EdgePrims (the contour line handles), as shown below. For additional info on customizing the contour labels/lines/faces read https://undocumentedmatlab.com/blog/customizing-contour-plots
% Create a simple contour plot
x = -2:0.2:2;
y = -2:0.2:3;
[X,Y] = meshgrid(x,y);
Z = X.*exp(-X.^2-Y.^2);
[C,hContour] = contour(X,Y,Z, 'ShowText','on');
% Update the text label colors
levels = hContour.LevelList;
labels = hContour.TextPrims; % undocumented/unsupported
lines = hContour.EdgePrims; % undocumented/unsupported
for idx = 1 : numel(labels)
labelValue = str2num(labels(idx).String);
lineIdx = find(abs(levels-labelValue)<3*eps, 1); %avoid FP errors using eps
labels(idx).ColorData = lines(lineIdx).ColorData;
end

  7 Comments

try to add a call to drawnow after the contour creation, before updating the labels.
thank you. What I was after.

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